This invention relates generally to the production of film and, more particularly, to the electrostatic pinning of a freshly cast web to the surface of a quenching drum.
In existing machines, film is produced by extruding a web of molten, polymeric, film-forming material onto a quenching drum and then advancing the quenched web through stretching and slitting stations to windups. The use of a charged electrode adjacent the freshly cast web for generating an electrostatic field which pins the web to the drum was disclosed by Owens et al. in U.S. Pat. No. 3,223,757. In U.S. Pat. No. 3,655,307, Hawkins disclosed the possibility of increasing the through-put of a casting machine by adding a grounded, insulated electrode and thereby increasing the pinning force. A modification of the two electrode system was proposed by Segransan et al. in U.S. Pat. No. 4,244,894. In Segransan el al., the second electrode is a grounded, uninsulated reflector. Attempts to increase the through-put with such systems have not been successful because of nonuniform pinning through the width of the web.